Coal liquefaction processes have been developed for converting coal to a liquid fuel product. For example, U.S. Pat. No. 3,884,794 to Bull et al. discloses a solvent refined coal process for producing reduced or low ash hydrocarbonaceous solid fuel and hydrocarbonaceous distillate liquid fuel from ash-containing raw feed coal in which a slurry of feed coal and recycle solvent is passed through a preheater and reactor in sequence in the presence of hydrogen, solvent and recycled coal minerals to increase the liquid product yield.
Reactor failure by coke deposition is a common problem in coal liquefaction systems. This problem can be so severe that liquefaction processing must be stopped for reactor cleaning, thereby causing a shutdown of the system and the usual problems attendant thereto. Techniques for continuous solds withdrawal from the reactor can not remove deleterious deposits which adhere strongly to the walls of the reactor vessel. Thus, it would be highly advantageous if solids deposition could be prevented, rather than merely eliminated after the solids are formed in the reactor, since physical removal means only remove solids which become dislodged from the internal reactor surfaces during normal operation.